From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH] [RFC] i2c: Don't wait for device release in
 i2c_del_adapter
Date: Thu, 15 Jan 2015 14:55:21 -0800
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To: Pantelis Antoniou <pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>
Cc: Jean Delvare <jdelvare-l3A5Bk7waGM@public.gmane.org>, Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>, Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>, Matt Porter <matt.porter-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-i2c@vger.kernel.org

On Thu, Jan 15, 2015 at 06:25:22PM +0200, Pantelis Antoniou wrote:
> Hi Greg,
>=20
> > On Jan 14, 2015, at 22:41 , Greg Kroah-Hartman <gregkh@linuxfoundat=
ion.org> wrote:
> >=20
> > On Wed, Jan 14, 2015 at 07:24:22PM +0200, Pantelis Antoniou wrote:
> >> I=E2=80=99ll try to dig around tomorrow and see what the real devi=
ce reference counts
> >> are, but my hunch goes like this:
> >>=20
> >> MUX
> >> +=E2=80=94- ADAPTER
> >>    +=E2=80=94 DEV.
> >>=20
> >> Mux remove method is called, i2c_del_mux_adapter is called on all =
the channels
> >> of the mux, calling in turn i2c_del_adapter which hangs on complet=
ion of the
> >> dev_released.
> >>=20
> >> The call to device_unregister never calls the device_type callback=
 (i2c_adapter_dev_release)
> >> because the reference count is not 1 at that point, someone else i=
s having another
> >> reference.
> >=20
>=20
> First of all, my head hurts. Tracking device references ain=E2=80=99t=
 easy. Is there some kind
> of debugging method you=E2=80=99d recommend for this?

You can turn on debugging for kobjects and the driver core if you want
to slow down your system log a bunch, but it can be helpful for trickie=
r
issues.  Or just sprinkle a few printks around.

> > I don't remember the i2c core code at all, that was a long time ago=
=2E
> >=20
>=20
> Bummer.

Do you remember code you wrote 12 year ago and haven't looked at for at
least 11?  Why expect others to as well? :)

thanks,

greg k-h